Might increase the fan size to move more air. As well, I'd go with a semi gloss on the ceiling in a bath. More moisture resistant. Forget the whole " mold is evil " thing , just kills it and paint over. As far as the air handler thing just make sure the drains run freely and all is well no matter the t-stat setting.
Mt Pleasant? My ex lives there.... Puts the Mount in Pleasant she does
better there than here